This invention relates to a method for operating a jet engine. When operating over enemy territory, a military jet aircraft is likely to come under attack by enemy air-to-air and surface-to-air missiles. These missiles may have any one of a variety of systems designed to direct a missile to intercept the aircraft under attack. One highly effective system uses a heat sensing device that allows the missile to home-in on the aircraft by detecting infrared radiation emitted by the aircraft.
The infrared radiation given off by a jet aircraft is largely the product of the smoky exhaust and very hot exhaust nozzle. Military jet aircraft in normal operation burn a hydrocarbon fuel. Such fuels emit smoke from the exhaust nozzle. The smoke is composed of very hot particles of carbonaceous material. As the hot particles pass from the engine they transmit at least a portion of their heat to the exhaust nozzle causing its temperature to rise. Both the exhaust nozzle and the carbonaceous particles act like black body radiators to give off energy in the infrared spectrum.